High performance lubricating compositions

ABSTRACT

An oleaginous corrosion-resistant lubricating composition comprising at least one alpha-olefin synthetic oil and effective amounts of metal salts of sulfonic acids/carboxylic acids, alkylated aromatic compounds as solubility modifiers, pour-point depressants, at least one antioxidant, and metal deactivators.

STATEMENT OF GOVERNMENT INTEREST

The Invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties thereon or therefore.

FIELD OF THE INVENTION

This invention relates to lubricating compositions and methods of using lubricating oils compositions that can be applied by spraying /brushing onto metal parts for long-term protection to minimize environmental effects particularly on aircraft parts. High performance, long lasting, preservative lubricating oils has been developed for use in internal airframe applications in the fleet to reduce the cost of corrosion maintenance and to improve the fleet readiness. This invention has focused on optimizing/blending a mixture of oils, corrosion inhibitors, antiwear agents, antioxidants, and other additive materials to form a high-performance lubricating oil. Lubricating oils are generally composed of a majority of base oil plus a variety of additives to impart desirable properties. This novel lubricating oil is intended for lubrication and protecting against corrosion of aircraft parts, certain small arms and automatic weapons and whenever a general purpose, water-displacing, low-temperature lubricating oil is required. Lubricants are typically used to separate moving parts systems. This oil has the benefit of reducing friction and surface fatigue, together with reduced heat generation, operating noise and vibrations. Currently, several formulations have been developed and tested on the requirements of MIL-PRF-32033 specification and corrosion prevention properties. Based on the testing results, the new formulations has shown superior performance compared to the existing MIL-PRF-32033 products.

BACKGROUND OF THE INVENTION

More specifically, corrosion is a costly factor in the Department of Defense. Aircraft and other weapon systems are old, and structural damage from corrosion is a life-limiting factor on some of these aircraft. One of the factors contributing to corrosion is that existing preservative lubricating oils have not proven to be effective for more than a few days and require repeated applications. MIL-PRF-32033 specification is currently used by DoD services as a preservative lubrication oil to maintain aircraft. MIL-PRF-32033 is a general purpose, water displacing, lubricating oil with preservative properties, and is intended for the lubrication and preservation of aircraft components. It is used mainly as a general-purpose lubricant in all applications where water displacement, water resistance, corrosion protection and/or low temperature performance is required.

The NAVAIR Corrosion Fleet Focus Team has indicated that the corrosion protection of lubricating oils is not sufficient and requires repeated applications. The goal of this invention was to develop high performance general-purpose lubricating oil products per MIL-PRF-32033 to reduce the maintenance cost and meet the fleet needs. This invention will benefit the Naval Aviation Enterprise (NAE) by providing a more efficient, cost effective and high performance lubricating oil for aerospace applications. The cost savings will be realized through reduced maintenance costs and enhanced mission readiness.

SUMMARY OF THE INVENTION

This invention relates to oleaginous or lubricating oil compositions consisting essentially of one or more poly-alpha olefin synthetic lubricating oil having a viscosity requirement that meets the specification of MIL-PRF-32033. The synthetic lubricating oil comprise effective amounts of metal salts consisting of a combinations of sulfonic acids and carboxylic acids, pour-point depressants comprising hydrotreated distillate heavy-paraffinic additives, one or more antioxidants such as the aromatic amines, metal deactivation, and alkylated aromatic compounds.

Therefore, it is an object of this invention to provide an oleaginous composition to protect against corrosion or rust of small arms, automatic weapons and aircraft parts.

It is another object of this invention to provide an oleaginous composition resistant to corrosion as a liquid.

It is a further object of this invention to provide an oleaginous composition and a method of using the composition to form a rust-resistant coating on metal surfaces.

These and other objects of the invention will become apparent by reference to the detailed description.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to oleaginous corrosion-resistant compositions and to the method of inhibiting corrosion or rust on various metal surfaces including metals such as aluminum, aluminum alloys and various ferrous metals. The oleaginous oil compositions of this invention consist essentially of, in parts by weight, from about 70 to 85 parts and preferably from 75 to 80 parts of at least one poly alpha-olefin synthetic lubricating oil, and various mixtures of said synthetic oils, 5.0 to 15 parts and preferably from 8.0 to 12 parts of oil soluble compounds comprising corrosion inhibitors selected from the group consisting of sulfonic acid/carboxylic acid metal compounds or complexes and mixtures of said sulfonic acid/carboxylic acid metal complexes with about 5.0 to 15 parts and preferably from 12 to 15 parts of an oil soluble alkylated aromatic compound as a solubility modifier, from about 0.1 to 1.0 part and preferably 0.3 to 0.5 parts of an oil soluble pour-point depressant, such as hydrotreated distillate heavy-paraffinic additives, from about 0.1 to 2.0 or 1.0 to 1.5 parts of at least one antioxidant, such as a diphenylamine, and from about 0.1 to 0.5 or 0.1 to 0.3 parts of a metal deactivator such as a triazole compound.

The preferred corrosion inhibitors are derived from the reaction of at least one sulfonic acid such a naphthalene sulfonic acid and at least one carboxylic acid such as a fatty acid with a metal or metal compound to form a metal complex. The corrosion inhibitors are derived from the stoichiometric reaction of a metal or metal compound such as an alkaline earth metal with a naphthalene sulfonic acid and a carboxylic acid preferably at least one or more of these acids to form the metal salts or complex.

The sulfonates may be prepared from sulfonic acids which are typically obtained by the sulfonation of alkyl substituted aromatic hydrocarbons as those obtained by the alkylation of aromatic hydrocarbons such as by alkylating benzene, toluene, xylene, or preferably naphthalene. Specific examples of the sulfonic acids include petroleum sulfonic acids, naphthalene sulfonic acids, such as the metal salts of dialkylnaphthalene sulfonic acids, wherein the alkyl group has from 1 to 12 and preferably from 7 to 10 carbon atoms, petroleum naphthene sulfonic acids, dodecylbenzene sulfonic acid, dinonylnaphthalene sulfonic acid and the like. These sulfonic acids are known in the art, and for the purpose of this invention, the weight of a sulfonic acid is the molecular weight divided by the number of sulfonic acid groups.

The carboxylic acids used in preparing the metal sulfonic acid/carboxylic-acid complexes include the aliphatic, cycloaliphatic, mono- and polycarboxylic acids. The aliphatic acids contain at least 1 and at least 12 carbon atoms. The aliphatic carboxylic acids can be saturated or unsaturated. Specific examples of the carboxylic acids include 2-ethylhexanoic acid, linolenic acid, substituted maleic acids, linoleic acid, lauric acid, oleic acid, ricinoleic acid, palmitic acid, and mixtures of two or more carboxylic acids. The preferred carboxy acids include the fatty acids having the formulas C_(n)H_(2n-1) COON or C_(n)H_(2n-3). The equivalent weight of these carboxylic acids is the molecular weight divided by the number of acid groups.

Preferably, the sulfonate/carboxylate metal salts or complexes are derived from alkaline earth metals such as calcium, barium, magnesium or the metal compounds. These metal neutralizing compounds include the metal oxides, hydroxides, carbonates, bicarbonates and mixtures thereof. These corrosion-resistant metal complexes are derived from the reaction of these metal compounds with stoichiometric amounts of the sulfonic acids and the carboxylic acids to form the metal salts or complex.

The pour-point depressants are known as lube oil flow improvers that lowers the temperature at which the fluid will flow or can be poured. Typical of these compounds which improve the flow temperature or fluidity of the oil includes the dialkylfumarate/vinyl acetate copolymers, polyalkylmethacrylates, esters of methacrylic acid, and the alkylated naphthalenes. Preferably, Cristol-PPD LX-150 (Hydrotreated Distillate Heavy-Paraffinic Compounds) are used as pour-point depressant additives to meet the pour-point requirements of MIL-PRF-32033 specification. It was necessary to add the pour-point depressant compound to the formulation to improve the oil's performance at low temperatures (−40° C.). The pour-point depressant is added to the corrosion-resistant compositions in amounts ranging from about 0.1 to 1.0 parts by weight, and preferably from about 0.3 to 0.5 parts.

The following is an example of the high performance lubricating compositions.

Lubricating Oil Formulation Example 1

Parts by weight 1. Synfluid PAO -2 cST (Boiling Point 223° C.) 70-85 (Poly-Alpha Olefin-Synthetic Fluid, Base Oil (Preferably) (1-Decene, Dimer homopolymer, hydrogenated) 75-80 And/Or Synfluid PAO -4 Cst (Boiling Point 414° C.) (Poly-Alpha Olefin- Synthetic Fluid, Base Oil) (1-Decene, homopolymer, hydrogenated) 2. NA-Sul CA -HT3  5-15 (Calcium Dinonylnaphthalenesulfonate/Carboxylate) (Preferably) (Corrosion Inhibitor)  8-12 3. Cristol-PPD LX-150 0.1-1.0 (Hydrotreated distillate heavy paraffinic compound (Preferably) (Pour-Point Depressant) 0.3-0.5 4. NA-Lube K R 007A  5-15 (Alkylated Aromatic Additive) (Preferably) 12-15 5. NA-Lube AO-130 0.1-2.0 (Nonylated Diphenylamine, Antioxidant) (Preferably) NA-Lube AO-242 and/or 0.1-1.5 (Butylated, octylated diphenylamine, Antioxidant) NA-Lube ADTC (and/or) (Methylene-bis-(dibutyldithiocarbamate, Antioxidant) 6. K-CORP ® NF-200 0.1-0.5 (Benzotriazole and Derivatives, Metal (Preferably) Deactivator 0.1-0.3

The kinematic viscosity requirements of ML-PRF-32033 specification is specified in Table 1.

TABLE 1 Kinematic viscosity, mm²/s) @ 40 degrees Celsius (° C.), minimum. 11 @ −40° C., maximum. 7,000 @ −54° C., maximum. 60,000

Neutral Salt Spray Test

The salt spray test for the oil compositions and various commercial products were performed in accordance with the ASTM B117 method. Table 2 shows the salt spray test results for the formulation compared to several commercial products qualified to MIL-PRF-32033. The new formulation showed superior performance compared to the existing MIL-PRF-32033 products. Steel panels coated with commercial products lasted only one to two days in the salt spray cabinet compared to four (4) days for steel panels coated with the new formulation. Further, aluminum panels coated with commercial products lasted less than five days in the salt spray cabinet while panels coated with the new formulation lasted more than 14 days.

TABLE 2 New Formulation FTM 5322 Corrosivity Test (240 hours) 50% relative humidity, 79° F. Pass FTM 4001.2 Salt Fog Steel  4 days Aluminum 14 days 4.2.5.5 Mil 32033 Film Characteristics Pass FTM 3458 Low Temperature Stability Pass 3.3.2.1 Mil 32033 Removability Pass

The new formulation was tested to the requirements of MIL-PRF-32033 specification and showed excellent results as shown in Table (3). The results in Table (3) indicate that the formulation meets or exceeds the requirements of MIL-PRF-32033 specification.

TABLE (3) Test Results of the Formulation to the Requirements of MIL-PRF-32033 Specification Specification New Test Method Limit Formulation Viscosity ASTM D445 @ 40 C., cSt, min 11 12.18 @−40 C., cSt, max 7,000 1509 @−54 C., cSt 60,000 Pour Point, C., max ASTM D97 57 −60 Low Temperature FTM 3458 Flow Flow Stability, −45 C. Freely Freely for 72 Hours Flash Point, C. min ASTM D92 135 178 Copper Strip Corrosion ASTM D130 2a 1a Wear Preventive, max ASTM D4171 1.0 0.43 Color of finished Fluid, ASTM D1500 7.0 2 Corrosiveness of ASTM D1748 No No Lubricating oil to Corrosion Corrosion Bimetallic Couple Oxidation Corrosion FTM 5308.6 No No Corrosion Corrosion

The intended use of the lubricating oil composition of this invention was described in Section 6.1 of the MIL-PRF32033 specification. The lubricating oil composition is intended for lubrication and protecting against corrosion of certain small arms and automatic weapons and whenever a general purpose, water-displacing, low-temperature lubricating oil is required. Oil becomes very viscous at low temperatures so that its use at temperatures below −40° C. is limited by a number of machine design factors and should be proved for any specific item application by testing before adoption. The availability of this composition in gas-pressurized containers will prove to be beneficial for use in areas difficult to preserve by existing procedures. This preservative oil should not be used however, to protect fuel systems and combustion chambers of engines which are preserved in accordance with standard procedures. Composition contains carboxylic acids which could react with certain metals present in the fuel system, forming soaps which could contribute to fuel filter plugging etc.

The developed preservative lubricating oil composition aims to reduce the cost of maintaining aircraft systems, and extend the life of aircraft platforms. Application of the newly developed composition will increase fleet readiness and provide significant cost savings to the end user. Expected Department of Defense benefits include decreased aircraft downtime due to fewer scheduled maintenance inspections and maintenance actions; increased aircraft availability; and reduced corrosion repair costs, hazardous materials, and maintenance man-hours.

While this invention has been described by a number of specific examples, it is obvious to one skilled in the art that there are other variations and modifications which can be made without departing from the spirit and scope of the invention as particularly set forth in the appended claims. 

1. A corrosion-preventing free-flowing lubricating composition consisting essentially of, in parts by weight, from about 70 to 85 parts of poly-alphaolefin synthetic lubricating oil, from about 5 to 15 parts of at least one metal salt of an alkylnaphthalenesulfonic acid/carboxylic acid compound, from about 0.1 to 1.0 part of an oil soluble pour-point depressant; from about 0.1 to 2.0 parts of at least one antioxidant, from about 0.1 to 0.5 parts of a metal deactivator and from about 5.0 to 15 parts of an alkylated aromatic compound.
 2. The composition of claim 1 wherein the free-flowing lubricant is a mixture of poly-alpha olefin oils having different viscosities and boiling points.
 3. The composition of claim 1 wherein the free-flowing lubricant is a mixture of poly-alpha olefin lubricating oils having a kinematic viscosity of 1509 at −40° C.
 4. The composition of claim 1 wherein the pour-point depressant comprises hydrated distillate heavy paraffinic compounds.
 5. The composition of claim 1 wherein the metal salt is an alkaline earth metal salt of a dialkylnaphthalenesulfonic acid/carboxylic acid compound.
 6. The composition of claim 1 wherein the alkylnaphthalenesulfonic acid/carboxylic acid metal salt compound is a dialkylnaphthalenesulfonic acid/carboxylic acid metal compound wherein the alkyl group of said sulfonic acid has two to twelve carbon atoms.
 7. The composition of claim 6 wherein the alkyl group of said sulfonic acid has nine carbon atoms.
 8. The composition of claim 6 wherein the metal salt is an alkaline earth metal salt of dialkylnaphthalenesulfonic acid/carboxylic acid compound.
 9. The composition of claim 6 wherein the pour-point depressant is an acrylic compound.
 10. The composition of claim 1 wherein at least one antioxidant is a diphenyl amine.
 11. A process of preventing corrosion of metal which comprises applying an effective amount of a corrosion-preventing free-flowing lubricating composition on said metal; said composition consisting essentially of, in parts by weight, from about 70 to 85 parts of a poly-alpha-olefin lubricating oil, from about 5 to 15 parts of at least one metal salt of an alkylnapthalenesulfonic acid/carboxylic acid compound, from about 0.1 to 1.0 part of an oil soluble pour-point depressant, from about 0.1 to 2.0 parts of an antioxidant, from about 0.1 to 0.5 parts of a metal deactivator and from about 5.0-15 parts of an alkylated aromatic compound.
 12. The process of claim 11 wherein the alpha-olefin synthetic oil is a mixture of synthetic oils having different viscosities.
 13. The process of claim 11 wherein the pour-point depressant is hydrotreated distillate heavy paraffinic compound.
 14. The process of claim 11 wherein the metal salt is an alkaline earth metal salt of the alkylnaphthalene sulfonic acid/ carboxylic acid compound.
 15. The process of claim 11 wherein the metal salt is a dialkylnaphthalene sulfonic acid/fatty acid metal compound.
 16. The process of claim 11 wherein the alkyl group of the alkylnaphthalene sulfonic acid has from 7 to 9 carbon atoms.
 17. The process of claim 11 wherein the metal salt of the acids is a salt of an alkaline earth compound.
 18. The process of claim 11 wherein the pour-point depressant is an ester of methacrylic acid.
 19. The process of claim 11 wherein the antioxidant is a diphenylamine
 20. The process of claim 11 wherein the lubricating composition has a viscosity of 1509 at −40° C. and the synthetic lubricating oil ranges from about 75 to 80 parts by weight of the composition. 